The present invention is directed to an attachment member unit to be driven into a hard receiving material by an explosive powder charge operated setting tool. The attachment member unit includes an axially extending shank with a load engagement means at its trailing end and a pointed tip at its leading end. At least the tip is laterally enclosed by a prestressing element formed of a sleeve part at its trailing end and a flange-like bearing part at its leading end with the bearing part having an outside diameter greater than the outside diameter of the sleeve part.
Attachment member units of the above type are driven into hard receiving materials, such as concrete, masonry, rock, steel and the like. Explosive powder charge operated setting tools are used for driving the attachment member units. A preferred use of such attachment member units is the fastening of connecting members to structural parts formed of hard receiving materials of the above-mentioned types. Such connecting members can be cable ducts, cable clamps, pipe clamps, insulation panels, suspensions and the like. The fastening of the connecting members is performed so that after the completion of the driving operation, a shoulder on a load engagement means abuts the connecting member and presses or stresses it against the receiving material.
The load engagement means of the attachment member unit can be shaped in various ways. For instance, it can be a head with its diameter projecting laterally outwardly beyond the diameter of the shank of the attachment member unit. Instead of a head, the load engagement means can be a thread projecting beyond the diameter of the shank and serving to receive a nut and also forming a shoulder.
The connecting members under consideration are formed mostly of plastics material, for reasons of economy and also in certain cases for reasons of insulation. The use of plastics material for the connecting member along with the type of attachment member unit using explosive powder charge operated setting tools creates certain problems. It must be assured that the connecting members are sufficiently pressed or stressed against the receiving material. This feature requires a defined setting depth of the attachment member unit, so that on one hand the danger of an inadequate stressing is prevented while on the other hand the danger of destruction of the connecting member is avoided.
It is difficult to assure a precise attachment depth when using explosive powder charge operated setting tools, the use of which is preferred in the present case for reasons of economy. This problem occurs because of the mainly non-homogeneneity of the receiving material and also because of the variations in the energy output of the explosive powder charges used. If the attachment member does not penetrate sufficiently deeply, the connecting member is insufficiently pressed against the receiving material. On the other hand, if the attachment member penetrates too deeply into the receiving material, there is the danger that the connecting member may be destroyed.
An attachment member unit is known from DE-PS 16 25 367 for avoiding the destruction of brittle materials where the unit has an initial pressing or prestressing element at its tip. The prestressing element has a flange-like bearing part at its leading end followed towards the trailing end by a sleeve part. The tip is located flush with the leading end face of the bearing part.
With this known attachment member unit the brittle material is intended to be prestressed by the prestressing element during the driving operation, so that it is not destroyed. In this known attachment member unit the tip begins to penetrate into the brittle material at the start of the driving operation before the prestressing element is able to generate an adequate prestress and the effect is unsatisfactory with the possible destruction of the brittle material taking place.